1. Field of the Invention
The present invention relates to a method of preventing defects by preventing electrical short-circuiting of bonding wires during processes that come after the wire bonding step.
2. Description of the Prior Art
In recent years, the increased integration level of large-scale integrated circuit devices has meant a decrease in the spacing between bonding wires. This has given rise to a fabrication problem of short circuits caused by contact between wires or between wires and lead frames, resulting from loops and bends in the wires. Specifically, one problem is that of short circuits caused by contact between wires occurring during the wire bonding process, and another problem is that of short circuits occurring during the handling of the semiconductor device in process operations that come after the wire bonding step.
A conventional way of solving such problems has been to use bonding wire that has been precoated with an insulating material. This method is illustrated in FIG. 4 and comprises using bonding wire 11 which has been given an insulative coating beforehand. To enable the bonding to take place, a plasma-arc or mechanical technique is used to remove the coating from the primary side bonding portion 12 and secondary side bonding portion 13.
However, while the use of a plasma-arc method makes it relatively easy to remove the coating from the bowl-shaped primary bonding portion, there has ben a lack of an effective method of removing the coating from the secondary bonding portion. Experiments have been conducted relating to the use of abrasion techniques and the like to expose the bonding surface, but in terms of reliability the bonding thus achieved is inferior compared to bonding effected after complete removal of the coating.
Furthermore, even when the coating is removed, a drawback has been the complex and time-consuming task removing the particles and fragments produced by the process of removing the coating. Moreover, high-cost wire bonding systems are idled for the extended time it takes to carry out this task of removing particles and fragments, thereby reducing equipment operation rates.
Through the development of the high-performance wire bonding systems now in use, the number of short circuits produced during the wire bonding process is extremely low. In fact, now the main task is the prevention of short circuits arising during the handling of devices following the wire bonding process.